One common means of framed concrete slab construction is achieved by pouring concrete onto decking constituted by sheets of corrugated metal. The metal decking is supported by steel girders such a suitably spaced beams. When metal decking is attached directly to the girders, it is common practice to attach headed steel studs to the girders, which studs extend upward through the metal sheets. These studs are usually welded to the beams. When concrete is poured onto the metal decking, it flows around the studs and after it hardens it forms a bond or lock with the girders by virtue of its solidifying around the head portions of the studs, a structurally more efficient assembly is achieved than if the girder acted independently. This is commonly known as "composite construction".
Another common method of framing concrete slabs consists of the use of standard web steel joists which support the metal deck and in turn bear or sit upon steel girders. In this type of assembly, the decking is usually attached directly to the joists and does not make direct contact with the girder, because the joists sit upon the top flange of the girder. As a result, there is an air space or gap between the bottom of the deck and the top flange of the girder. Consequently, no direct bond between the concrete and the girders can be taken advantage of as in the structure which utilizes the metal studs for this purpose. To achieve composite action between the girder and concrete slab when joists are utilized, in one type of construction, the metal deck is discontinued over the girder and sloped or pitched down to the top flange of the girder in order to establish contact between the girder and concrete slab. Another current practice is to eliminate the metal decking and form the slab on plywood, using special joists which protrude into the slab. This also results in connection of the girder with the concrete slab. Since connection is now established, studs may additionally be utilized to achieve composite action between the steel girder and concrete slab.